<p>As a green mining strategy, the cemented backfill mining method has been extensively used in the most mineral resource recoveries due to its efficient utilization and environmental protection. In order to evaluate the ability of the backfill to bear dynamic loads under actual mining conditions, it is necessary to investigate the dynamic mechanical properties of the in situ backfills. In this paper, a series of impact tests are performed on the in situ backfill specimens obtained from various drilling depths under a strain rate range of 30 to 180&#xa0;s⁻¹, using a split Hopkinson pressure bar (SHPB) system. The dynamic stress–strain curves reveal the deformation process of the in situ backfills under impact loading, characterized by three distinct stages: elastic deformation stage, compaction yield stage, and failure stage. The dynamic mechanical properties, including dynamic elastic modulus, peak stress, and dynamic increase factor (DIF), are investigated in detail, which are related to the strain rate and drilling depth. The results illustrate that the strain rate has an obvious enhanced effect on the dynamic mechanical properties of the in situ backfill. The drilling depth reduces the elastic modulus and peak stress while promoting the DIF value under high strain rate loading. Furthermore, the failure characteristics of the in situ backfills after impact loading exhibit four different modes, i.e., fracture, block, fragmentation, and crushing from low strain rate to high strain rate. This research can provide a useful and valuable guidance for evaluating the performance and effectiveness of the cemented filling mining method in practical applications.</p>